As shown in FIG. 1, there is conventionally known a method of manufacturing a hollow structural member in which: a temperature control apparatus 23 is provided inside a hermetically sealed vessel 22 on an upper part of a material coating apparatus 21; a substrate 24 for production of a hollow structural member in which a multiplicity of recesses 24a are arrayed on its surface is set in position on the temperature control apparatus 23; a plastic deformation material for forming therewith a hollow structural member as a honeycomb structure is caused to be ejected from a material ejection apparatus 25 toward the surface of the substrate 24 for production of a hollow structural member; the material coating apparatus 21 is rotated to thereby form, on the surface of the substrate 24 for production of a hollow structural member, a substantially uniform plastic deformation film 26; the gas pressure inside the hermetically sealed vessel 22 is reduced; and the plastic deformation film 26 is thus caused to be expanded and drawn by the pressure of the gas stored in each of the recesses, to thereby manufacture a hollow structural member having a multiplicity of hollows (see, e.g., patent document 1).
The term honeycomb structure means in the invention not only the one having hexagonal shape of holes but also includes the ones having square and pentagonal holes and refers, irrespective of the shape, to the sheet-like members as a whole having a plurality of hollows.
(Patent document 1) JP-A-2007-98930 (page 15, FIG. 7, FIG. 8)
In Patent Document 1, there was obtained a hollow structural member in which the pitch distance between the center of a hollow to the center of another hollow is 35 μm. In case the pitch distance between the center of a hollow to the center of another hollow becomes 30 μm or below, it is difficult to manufacture a hollow structural member in this manufacturing method. The reasons are explained hereinbelow.
Let the point of time at which the plastic deformation film 26 was formed on the surface of the substrate 24 for production of a hollow structural member be t=t0 (see FIG. 2). After a lapse of time t=t1, there will disappear the gas storing space that is defined by the recess 24a and that has the gas pressure P1 (see FIG. 3). As a result, the gas can no longer be expanded at the gas pressure P0 under the reduced pressure conditions.
According to the Yung-Laplace's equation, the pressure of a bubble is generally proportional to the surface tension of the substance enclosing the bubble and is inversely proportional to the radius of the bubble. For example, in case of a bubble in the water, when the diameter is 100 μm, the pressure difference between the pressure of the bubble and the external pressure is about 3 kPa. Here, if the diameter is made smaller to 10 μm, the pressure difference between the pressure of the bubble and the external pressure will become about 30 kPa. If the pressure of the bubble becomes higher, the solubility of the gas into the water increases, with the result that the gas will be molten into the water. Then, the size of the bubble becomes smaller and, as a result, the pressure becomes still higher and the gas will be dissolved into the water. The smaller becomes the size of the bubble, the higher becomes the speed acceleratingly, thereby finally resulting in disappearance of the bubble.
It is considered that the same kind of phenomenon is taking place with the plastic deformation film 26. In this case, if the pitch distance becomes smaller, the pressure in the gas storing space increases due to the surface tension of the plastic deformation film. In case the gas inside the gas storing space is plastic material that forms the plastic deformation film 26, or in case the substrate 24 for production of a hollow structural member is a gas-permeable material, they will be dissolved into the gas-permeable material, and the gas is discharged to the atmosphere at a low pressure P0. Finally, the gas storing space will entirely be filled with the plastic deformation material after a lapse of time.
As a result, there is a disadvantage in that the hollow structural member having the pitch distance of the hollows of 30 μm or below cannot precisely be formed.